Propeller slip clutch



April '1, 1953 M. E. HARTZ 2,633,923

/ PROPELLER SLIP CLUTCH Filed June 28. 1950 ya@ @JM y JQZZOr/yegs 3 rotatably secured therewith. The inner diameter of spring 2l is larger than shaft 2 to provide ample clearance for the clutch action, as will be described.

The outer diameter of spring "2l is larger than the inner diameter of bushing 9 to provide the necessary frictional engagement and drive between shaft 2 and. propeller I.

The outer face of spring 2| is preferably iiat to provide a maximum frictional area of contact with bushing 9.

The spring 2I winds in a direction from. its fixed end held in notch 22, opposite to the direction of rotation so that rotationot collar I3 tends to pull the spring inwardly from clutch contact with bushing 9. The resilience of the spring and its resistance toV inward Wind provides the necessary clutch engagement normally existing between it and bushing 9, to drive the propeller I'.

In the assembly of clutch unit 4, collar I3 and spring VPZI are first inserted Within bushing 9. Plate I may be installed immediately on shaft 2, and propeller I with the spring-clutch unit 4 is then mounted on plate I0 and shaft 2 and secured thereon by nut I4, as described.

According to the invention, the spring-clutch member 2I provides for the accurately predetermined limited transmission. of torque from shaft 2 to propeller I and is disposed in .hub 5 of the propeller so as to be assembled and vdisassembled therewith as a unit. The limited torque transrr'iission provided by spring 2I affords an initial overload protection of the propeller against damage which is determined by the resilience ofl the spring and generally irrespective of the frictional engagement of the clutch parts.

The initial frictional engagement between spring 2I and bushing 9 is thus readily calculated and predetermined according to the preloading of spring 2 I during assembly of the clutch unit.

A feature of the invention resides in thel combination of the clutch elements with the propeller which includes hub 5, bushing 9, collar' I3 and spring 2l, as shown in Fig. 4. By reason of the preloaded condition of spring 2 I' the propeller and clutch unit- 4 is handled. and' assembled on shaft 2 as a. unit with. built-n overload protection.

The operation of, thek clutch upon overloadis effected when the' torque transmitted. from` coilar I3 through spring 2I to the propeller exceeds the torsional capacity of the spring. When the propeller isk subject to overload spring 2I winds on shaft 2 beginning with the end connected to collar I3 and is radially contracted and progressively withdrawn from contact with bushing 9, as shown in Fig. 3, until the portion of spring remaining in frictional engagement with bushing 9 is reduced` so as 'to be ineiectual and readily subject to the slippage necessary to prevent damage to the propeller. Bushing 9 engaging plate VIII prevents axial loading of the clutch unit 4 either bythe propeller thrust vor by tightening 'nut `I 4. The clutch unit 4 forms an integral part ofi propeller l and is not readily disassembled. Furthermore, 'as will be noted, clut'oli'funi-tv 4'is not capable of adjus'tment upon shaft 2 -as in 'securing propeller 4 capacity of the unit, as may be predetermined, cannot be altered.

The load capacity of the clutch unit 4 is easily tested as on a jig, not shown, so that each propeller I before delivery may be so tested and the adequate protection of the propeller against damage assured or guaranteed.

Various embodimentsV ofIk the invention may be employed' within the scope of the following claim.

I claim:

In an outboard motor, a propeller shaft havingk a threaded end and an annular shoulder facing said end and spaced therefrom, splines formed in said shaft .between said shoulder and said threaded end portion, a circular plate member disposed on said shaft against said shoulder, an internally splined circular collar tting the splines of said shaft so as to be rotatably secured thereon, a propeller including a hub having a central, stepped axial bore rotatably supported at opposite ends on. said plate and said collar, a hub mounted on the threaded end of said shaft, a tab washer fitting said splines and disposed between said propeller hub and said nut to secure the latter on the threaded end of said shaft, a friction washer disposed between said tab washer and the corresponding end of said propeller hub, a bushing tightly disposed within the larger portion of the stepped bore of said propellerl hub, one end of said bushing being disposed in contact with said plate and limiting the forward position of the propeller upon said shaft. and a spring-clutch element disposed within said bushing in frictional engagement with the inner surface thereof and extending in a helix about said shaft between said plate and said collar, the end of said spring adjacent said plate being free and the opposite end of said spring being engaged within a corresponding notch formed in the periphery of said collar whereby the rotation of said shaft is transmitted from said collar to the spring, said spring being disposed within said bushing under predetermined torsional stress to maintain a minimum radial frictional engagement with said bushing and driving connection with said propeller, and said spring being wound in a rotational direction from said fixed end whereby said spring upon overload is contracted around said shaft and withdrawn from frictional engagement with said bushing to allow slippage between said spring and said bushing and protect said propeller against damage.

e MARVIN E. HARTZ.

REFERENCES CITED The following references are of record in the fileV of this patent:

UNITED STATES PATENTS Number Name Date 2,125,270 Conover Aug'. 2, 1938 2,185g45'? Conover Jan. 2, 1940 FoRErG-N PATENTS Number Country Date 6,345 Great Britain 1907 601,970 Germany 1 1934 

